Euphorbia decidua

Origin

Euphorbia decidua P.R.O.Bally & L.C.Leach is endemic to a small area of the central watershed of Zimbabwe, with the type locality on serpentine hills near the Great Dyke (Africa). It was described by Bally and Leach in the mid-twentieth century from plants collected in seasonally dry miombo woodland, and it is regarded as one of the more unusual medusoid euphorbias in serious caudex collections for its habit of shedding its branches each year.

Habitat

In its natural environment, this species is a specialist of seasonally dry miombo and mopane woodland on ultramafic serpentine soils, where it grows among grass tussocks and low scrub at altitudes around 1100–1500 meters above sea level. Rainfall arrives in a single summer wet season followed by a long cool dry winter. The plant passes the unfavourable months as a dormant underground tuber, sending up a fresh rosette of branches at the start of each rains.

Description

Euphorbia decidua is a small geophytic medusoid euphorbia whose annual cycle of shedding its entire branch rosette makes it one of the most behaviourally distinctive species in the genus.

Caudex & Stem: Below ground sits a thick, tuberous main stem that functions as the perennial storage organ. From its apex a rosette of slender, decumbent, segmented branches is produced each growing season; these branches die back and abscise at the end of the rains, leaving the tuber bare through winter.

Roots: A coarse, woody taproot descends from the tuber into the rocky serpentine subsoil, with finer laterals that exploit the brief moist season.

Spines & Stipules: The branch segments carry paired short stipular spines at each tubercle, forming neat horn-like pairs along the ribs. The spine arrangement, together with the deciduous branches, separates this species from the related Euphorbia clava and Euphorbia gorgonis.

Flowers: Yellow-green cyathia are produced at the branch tips in the warm wet months, the characteristic cup-shaped true flowers of the genus, small and tidy against the dark green segments.

Cultivation: Grow in a deep mineral mix that keeps the tuber partially exposed for display, water generously while branches are present, and withhold water almost completely once the branches yellow and drop. Bright light and good air movement are essential, and the plant is frost-tender.